Non-puckerable seam



c. E. REEsE NoN-PucxERABLE sEAM mea March 2v, 1957 May 24, 1960 OONVENTIONAL SEAM 4 INVENTOR CECL E. REESE United States Patent O N ON-PUCKERABLE SEAM Cecil E. Reese, Kinston, N.C., assignor to E. I. du Pont de Nemours and Com an Wilmin t poration of Delaware P y g im, Del., a cor Filed Mar. 27, 1957, ser. No. 648,941 1 claim. (ci. z-z1s) treatment of the seam subsequent to laundering. The invention also 4relates to an improved sewing process in accordance with which such seams can be prepared.

The causes of puckering in stitched fabrics have been studied 'in great detail, and it has been found that numerous factors `contribute to this problem. In some causes the two layers of fabric to be stitched together may be fed through the sewing machine at unequal rates, with the result that compensation occurs in the form of gathering or puckering of the stitched fabrics when they are free of machine tension. The weight, construction, and other characteristics of the fabric also influence the observed amount of pucker, so that in some cases a tightly constructed fabric may be observed to undergo puckermg when it is fed through a sewing machine even when no sewing thread is used. The direction of the seam across the fabric with respect to warp and filling yarn is also a yfactor in many instances. However, the most significant factor in seam puckering is the contraction of the sewing thread in the seam, and hitherto this factor has been the most diiiicult problem in producing stitched fabrics free from pucker.

One cause of sewing thread contraction is the tendency of the sewing thread to stretch as it is being sewn into the seam in response to the tension which is placed upon the thread during sewing. After the stitch has been formed and the tension has been relaxed, the thread recovers its original length over a period of time, resul-ting in progressive puckering of the seam. Another -important cause of contraction in sewing threads is the shrinkage of the thread in the seam during laundering and other textile treatments. Pre-shrinking of the sewing thread is used as an expedient, but in practice it has been found that the strains induced in the thread during the sewing operation cause the thread to undergo further shrinkage during laundering. It has also been proposed to use a plied sewing thread containing a water-soluble component ply .to create slack in the other component ply after laundering, but such threads have been found to be quite sensitive to humidity and difcult to handle in the sewing operation, aside from the loss involved in discarding the watersoluble component ply.

Itis usually found that ironing improves the appearance of puckered seams. observed that the seam again becomes -puckered after laundering, so that it is necessary to iron the seam after each laundering in order to make it smooth again. New synthetic fabrics have been developed which do not in themselves require ironing subsequent to laundering to remove wrinkles; however, it has beenV found that the problem of seam puckering after laundering also extends `,t9 these fabrics,v` even when the sewing thread which is In most instances, however, it is ice used -is of the same synthetic material as the fabric itself. For -this reason, garments otherwise suitable for laundering without necessity Yfor subsequent ironing have hitherto suffered yfromrthe `defect that the seams have remained puckered unless ironed after each laundering. q It is an object of this invention to provide a seam comprising layers of fabric stitched together by at least one thread, said seam being characterized by smoothness and freedom from pucker with a minimum of treatment subsequent to the sewing operation. Another object of the invention is to provide such seams which are further characterized in that the observed amount of pucker in the seam remains at a permanently low level during normal use involving intermittent laundering. A further object is to provide an improved sewing process by which such seams can be provided in a rapid and easy manner. Other objects will become apparent in the following description and claim.

It has now been found that, in a seam comprising 1ay Y ers of fabric stitched together by at least one thread and characterized in that on at least one side of said seam each thread normally visible has a yield strength for 15% permanent deformation of less than about 0.1 gram per denier (g.p.d.) at C., the amount of pucker attributable to the sewing thread is reduced to a very low level lupon treatment of the seam at temperatures of 160 C. A preferred'embodiment of the invention comprises a seam on at least one side of which each Ithread normally visible has a yield strength for 15% permanent deformation of less than about 0.05 g.p.d. at 160 C. Another embodiment of the invention comprises a seam on at least one side of which each thread normally visible is characterized by at least 2% spontaneous and irreversible extension in length under zero tension at 160 C. A highly preferred embodiment of the invention comprises a seam on at least one side of which each thread normally visible is characterized by at least 2% spontaneous and irreversible extension in length under -zero tension at 160 C., the yield strength for a total of 15 permanent deformation being less than about 0.05 g.p.d. at 160 C.

The products of the invention may be formed by known sewing techniques, in which at least one thread 1s .stitched through the fabric layers along the line in which 1t 1s desired to form a seam joining the fabric layers. Under conditions of practical usage sewing is normally carried out with the aid of a sewing machine in which the stitches uniting the fabric are formed by threads from each side of the seam, one of the threads (known as the needle thread or top thread) being continually forwardedthrough the eye of the needle during the sewing operation, and the other thread (known as the bottom thread or bobbin thread) being fed from the other side of the fabric layers, frequently from a bobbin. Occasionally it is deslred to form seams using a multiplicity of needle threads or bottom threads or both. In commercial sewing the needle thread and bottom thread are maintained under controlled tension to form a balanced stitch with the stitch knot lying between the fabric layers, so that the needle Y thread is normally visible only from the top side of the finished seam as it passes over the top fabric layer between stitches and, similarly, the bottom thread is norl 3 more than about 1500 stitches/minute, by using threads having the required low yield strength at 160 C. in both the needle and the bobbin. In another embodiment of the invention, the product comprises a seam in which each thread normally visible on one side of the seam has al yield strength for 15% permanent deformation of less than about 0.1 g.p.d. at 160 C., each thread normally visible on the other side of the seam having a higher yield strength at 160 C. Surprisingly, in this casealso the product is characterized by freedom from pucker after exposure to temperatures up to about 160 C.

So far as the product is concerned, either the needle thread or the bottom thread may have the required low yield strength at 160 C. However, with respect to the process for producing the seams, highly beneicial results are achieved when the low yield strength thread is used as the bottom thread. Accordingly, in a preferred process embodiment of the invention, a seam uniting at least two layers of fabric is formed by feeding the layers of fabric in substantial alignment through a sewing machine equipped with means for forming a continuous series of stitches with at least one bottom thread and at least one needle thread, each bottom thread being characterized by a yield strength for 15% permanent deformation of less than about 0.1 g.p.d. at 160 C. The needle thread may be any of the known sewing threads characterized by sutlicient ,toughns under normal sewing conditions to achieve a low incidence of breakage. When the process is performed in this way, commercial sewing speeds of up to 5,000 stitches per minute or even higher are easily attained. Surprisingly, the incidence of breaks during sewing is lower when the process is performed in this way than when identical threads of high yield strength are used in both the needle and in the bobbin. The as-sewn seams prepared in this way also exhibit a much lower level of pucker than seams prepared with identical threads of high yield strength in both the needle and in the bobbin.

The yield strength for 15% permanent deformation of a thread at a given temperature is defined herein as the force which, when applied to the thread at the given temperature, is suflicient to cause in the thread a permanent elongation, measured at room temperature (25 C.), of at least 15 The yield strength defined in this way is determined by a series of experiments in which known lengths of the samples of the thread to be tested are subjected to constant tension at the given temperature for 3 minutes, following which the tension is released and the samples are again exposed to the given temperature for 3 minutes while free of tension, the samples finally being cooled to room temperature and their new lengths measured. The percentage elongation, or deformation, of the samples at varying levels of tension are then plotted graphically to estimate the tension required for 15 permanent deformation. Yield strengths referred to herein are those measured at 160 C., which is regarded as the maximum desirable temperature to which many textile fabrics should be subjected and is therefore also the maximum temperature to which the threads in many seams will be subjected. In accordance with the present invention, it has been found that threads having a yield strength for 15% deformation of less than about 0.1 g.p.d. at 160 C. produce smooth seams upon ironing at 160 C. and that the level of pucker then remains low after repeated launderings; while threads having a yield strength for 15 deformation of substantially higher than 0.1 g.p.d. at 160 C. produce seams in which, despite an initial ironing treatment, the pucker reappears after each laundering. Still better results are obtained by employing a thread having a yield strength for 15% deformation of less than about 0.05 g.p.d., especially one which exhibits at least 2% spontaneous and irreversible extension in length at 160 C., i.e. one which has a nominal yield strength for 2% permanent deformation of zero.

The value of the yield strength for a given thread will vary depending upon the temperature at which it is measured. In both natural and synthetic threads the yield strength falls off as the temperature is increased', however, the `yield strength for deformation has hitherto usually been greater than 0.1 g.p.d. at 160 C. for commercial samples of yarns or threads marketed for textile uses, especially for sewing thread use. By various techniques, however, threads can be prepared which exhibit a yield strength for 15% deformation of less than 0.1 g.p.d. at 160 C., especially threads composed of synthetic polymers such as polyethylene terephthalate or polyacrylonitrile prepared by suitable techniques.

It has been found that threads composed of certain polymers, such as polyethylene terephthalate, can be prepared in such a way that they exhibit the phenomenon of spontaneous and irreversible extensibility when they are heated. Such threads have a nominal yield strength value of zero, since permanent elongation of the thread occurs without any tension being applied to the thread. After these threads have undergone the full amount of spontaneous and irreversible extension which is inherent in them, a further amount of permanent deformation in the threads may be obtained by applying tension to the ends of the threads, and the yield strength value during this second range of deformation may also be found to be at a relatively low level.

For best results in obtaining seams having a permanent low level of pucker after the initial heat treatment at C., the sewing thread which is used should exhibit a spontaneous extension in length of at least 2% under zero tension at 160 C. and should be capable of a total of 15% permanent deformation at 160 C. with a tension of no more than 0.05 g.p.d. Included among such threads are those which exhibit a spontaneous extension in length of 15 or higher under zero tension at 160 C.

Seams sewn in accordance with the present invention have great utility in garments and other textile products, since the seams in the manufactured articles become sub stantially free from pucker by employing standard textile nlshing techniques, such as ironing, involving the application of heat at temperatures of 160 C. or even lower in some instances. The fact that heat treatments effective to eliminate the pucker in the finished seams can be carried out at temperatures of 160 C. and lower is irnportant, since damage occurs in many fabrics when they are heated above 160 C., and this temperature is therefore regarded as the maximum desirable ironing temperature. Ironing or pressing at a temperature on the order of 160 C. is the preferred manner of removing any pucker exhibited by the seams as sewn, although other forms of heat treatment are frequently elective. Temperatures higher than 160 C. may be used if the fabric permits, although elevated temperatures are not required for the purpose of the invention. Lower temperatures are frequently effective, especially with threads exhibiting a high degree of spontaneous extension in length.

It is believed that the low yield strength of the threads, on the order of 0.1 g.p.d. or lower at 160 C., allows the threads to elongate and also to bend to form a more compact stitch in response to the strains in the puckered seam and so to allow the seam to straighten itself, although this statement is not intended to be limiting. Since the threads have attained their new positions without undergoing appreciable internal strain, there is little or no tendency for them to shrink during subsequent laundering steps and the seam remains substantially free from pucker. -It is observed that, Within the yield point range lying below 0.1 g.p.d., the threads having the lower yield point values also exhibit the lower degree of puckering inthe finished seam, and that the lowest degree of puckering is attained when threads characterized by spontaneous and irreversible extensibility amounting to at least 2% upon heating are used. Surprisingly, despite the low yield point value of the threads in the seam, seams prepared Vin accordance with the present invention are found to be fully adequate in strength and durability in nished tion with sewing threads of low yield strength, and sub- A sequently subjected to "heat treatmentv followed by laundering, and

Figure 2 is a magnified sectional elevation of one stitch in a seam prepared, heat-treated, and laundered in the same way as the seam shown in Figure 1, except that each of the threads used in the stitches have a highY yield strength.

In the drawings, superposed layers 1 and 2 of textile fabrics have been stitched together on a conventional sewing ,machine to form a seam, following which the seam has been ironed at 160 C. and subsequently laundered. Figure 1 illustrates the appearance of one of the novel seams of the invention, in which the stitches have been formed by using in the sewing machine in both the needle and inthe bobbin threads 3 characterized by a yield strength for deformation of less than 0.1 g.p.d. at 160 C. As shown in the ligure, the threads are bent with low radii of curvature at the approaches 5 to fthe stitch loop and the crossover 6 in the stitch loop, with the result that the stitch loop occupies a minimum of space as it passes through the fabric layers and the distortion. caused by the pushing aside of the yarns in the fabric is minimized. The seam exhibits little or no pucker. Figure 2 illustrates the appearance of a seam in which conventional threads 4 characterized by high yield strength have been used in both the needleand in the bobbin. As shown in the figure, the approaches 7 to the stich loop and the crossover 8 in the stitch loop in each thread have high radii of curvature, with the result that the stitch loop occupies more space as it passes through the fabric layers than the corresponding stitch loop of Figure 1, and the distortion caused by the pushing aside of the yarns in the fabric is correspondingly greater. The seam exhibits a high degree of pucker, such that ironing of the seam would be required to make it relatively smooth again. A

Linear terephthalate polyester sewing threads having a spontaneous and irreversible extensibility of at least about 2% at 160 C. are preferred for preparing seams in accordance with the present invention. By linear terephthalate polyesters is meant linear polyesters in which at least 85% of the recurring structural units are units of the formula -o(oHu0ocoowherein n represents an integer within the range of 2 to 10. Linear terephthalate polyesters and copolyesters, such as polyethylene terephthalate and copolyesters thereof (wherein n is equal to 2) can be readily prepared in the form of threads exhibiting spontaneous and irreversibley extensibility. For example, an oriented polyethylene terephthalate thread, preferably one which is substantially amorphous, may be exposed to water or steam at 100 C. for an exposure time on Ythe order of about 0.1 second to shrink the thread at least preferably 40% or more. In this way threads exhibiting spontaneous and irreversible extensibility of 160 C. amounting to between about 2% and 20% or even higher may be produced. l Those threads having a spontaneous extensi-y bility amounting to' between 2% and 15 exhibit a yield strength for a total of 15% permanent deformation of less than about 0.1 g.p.d. at 160 C. It is observed that spontaneously extensible polyethylene terephthalate threads give strong seams, despite their low yield strength at 160 C., and the durability of the seams is excellent threads lto attackby chemicals, mildew, and other agents injurious to other textilematerials.

- Threads characterized by low yield strength, but which do not actually exhibit spontaneous extension in length, may be produced inV various ways. For example, in the case of polyethylene terephthalate threads, a thread having a highdegree of spontaneous extensibility mayV be heated, especially in ,the presence of certain chemical agents such asby dyeing the thread in the presence of a carrier, to cause the thread to undergo all of the spontaneous extension in length` of which, it is capable. The resulting thread, Whichisl no longer spontaneously extensible, is characterized by Ia yield strength of less than about 0.1' g.p.d. at 160. C. Other synthetic polymers may be processed lin known ways to form` threads characterized by low yield strength at 160v C. or below.

The following examples qwill serve to illustrate the invention, although they are not intended to be limitative. In the examples,rthe degree of pucker` in the seams is measured quantitatively as the amount by which the ,seamsr must be stretched top-make them smooth and free from pucker, expressed asa percentage figure and designated as the pucker rating. The pucker rating is determined by clamping `irmlya 10-inch length of seam with a fixed clamp at one end anda movable cla-mp at the other end, stretching the seam by moving the movable clampjust sufliciently to remove any trace of pucker in the seam, measuringthe extension in length of the seam, and expressing the extension in length as a percentage of the original length of the seam.

Example l Polyethylene terephthalate having an intrinsic viscosity of 0.57 is spun at 295 C. through a spinneret having 27 oriiices,.e`ach 0.009 inch in diameter, and the yarn is wound up at a speed of 1200 yds/min; The yarn is found to have a denier as-spun of 135. The yarn is passed from a supply package through a bath of water at 25 C. and over a sponge to leave a thin uniformv film of water on the yarn, after which it is passed around a feedV roll, around a draw pinv 1.6 inches in diameter maintained at a temperature of 100 C., and then around a draw roll, finally being wound up on a suitable package. The speed at the draw roll is 545 yds/min. and the draw ratio is 2.937. The drawn yarn is then passed from a feed roll through la steam oven l2 inchesv in length maintained at 100 C., the yarn entrance and exit being one-half inch in diameterr and steam at 100 C. being introduced along the bottom of the oven at a rate suicient to keep the oven lled with steam. The yarn speed at the entrance to the oven is 268 yds/min. and at the exit'of the oven is 150 yds/min., corresponding to a shrinkage of 44% in the yarn as it passes through the The yarn is then twisted 2l turns per inch inthe S owing tothe resistance of the polyethylene terephthalate direction and three strands ofthe twisted yarn are plied together with 13 turns per inch in the Z direction. The

resulting thread, designated hereinafter as Thread-A, exhibits 22% spontaneous and irreversible extensionin length, or permanent deformation, when it is heated at 'l'60,C. for 6 minutes without any tension being applied to the yarn. 1 @Thread B is prepared by twisting standard, hightenacity, 34-lament, 70-denier polyethylene terephthalate yarns 21.2 .turns per inch in the S direction and plying 2 such yarns 17.1 turns per inch in the Z direction to produce a 150.7 deniersewing thread. When testedundentension at 160 'C., Thread B exhibits only 0.2% permanent deformation under a tension of 0.1 g.p.d. and only 1.3% permanent deformation under a tension of 1.0 g.p.d.

Thread A is used as the bobbin thread and Thread B is used as the needle thread in a standard single needle lock stitch sewing machine (designated as a Singer model 241-12 with a Sirnanco needle No. 14) to sew a seam joining two layers of nylon taffeta fabric, the seam running in the warp direction in each of the fabric layers. The nylon taeta fabric has a Weight of 2.6 ounces per sq. yard and its construction is 154 ends x 92 picks, woven from 34lament, 76-denier polyhexamethylene adipamide yarns having 11 turns per inch in the Z direction in the warp and 8.4 turns per inch in the Z direction in the lling. The seam contains 18 stitches per inch and the machine is operated at the rate of 5,000 stitches per minute. The seam, which has an as-sewn pucker rating of 0.95%, is pressed with a steam iron at 160 C., whereupon it becomes quite smoothv (pucker rating 0.0%). The seam is then subjected to cycles of laundering in 160 F. water and drying at 210 F. without subsequent ironing. At the end of this treatment the seam has developed a pucker rating of only 0.60%. In a control experiment, in which Thread B is used both as theneedle thread and as the bobbin thread, the as-sewn seam has a pucker rating of 1.73%, the pressed seam has a pucker rating of 1.45%, and the laundered seam has a pucker rating of 2.32%.

In a similar experiment, low pucker ratings are obtained by substituting for the plied thread dignated as Thread A a polyethylene terephthalate singles yarn having a twist of only 5 turns per inch in the Z direction but having the same denier and the same degree of spontaneous extensibility as Thread A. In still an other experiment, low pucker ratings are obtained by sewing a seam at 1500 stitches per minute using Thread A as both the needle thread and the bobbin thread.

Example II Polyethylene terephthalate is spun and drawn as described in Example 1, following which it is passed through the 100 C. steam oven of Example I at an entrance speed of 234 yds/min. and an exit speed of 150 yds/min., corresponding to a shrinkage of 36% in the yarn as it passes through the oven and an exposure time of 0.13 second in the steam. The yarn is then twisted and plied as described in the preparation of Thread A in Example I. The resulting thread, designated as Thread C, exhibits 5.9% spontaneous and irreversible extension in length, or permanent deformation, when it is heated at 160 C. for 6 minutes without any tension being applied to the yarn.

Thread D is prepared by twisting standard, hightenacity, 34-lament, 70-denier polyethylene terephthalate yarns 23.6 turns per inch inthe S direction and plying 3 such yarns 20.2 turns per inch in the Z direction to produce a 245.4 denier sewing thread. When tested under tension at 160 C., Thread D exhibits only 0.2% permanent deformation under a tension of 0.1 g.p.d. and only 1.3% permanent deformation under a tension of 1.0 g.p.d.

Thread C is used as the bobbin thread and Thread D is used as the needle thread in a standard single needle lock stitch sewing machine (designated as a Singer model 251-2 with a Simanco needle No. 14) to sew a seam joining two layers of the nylon taffeta fabric of Example I. The seam contains 18 stitches per inch and the machine is operated at the rate of 3500 stitches per minute. The seam, which has an as-sewn pucker rating of 2.22%, is pressed with a steam iron at 160 C., whereupon its pucker rating drops to 0.20%. The seam is then subjected to 5 cycles of laundering in 160 F. water and drying at 210 F. without subsequent ironing. At the end of this treatment the seam has developed a pucker 8 rating of only 1.33%. In a control experiment in which Thread D is used as both the needle thread and as the bobbin thread, the as-sewn seam has a pucker rating of 2.38%, the pressed seam has a pucker rating of 0.73%, and the laundered seam has a pucker rating of 2.08%.

Example III Thread A of Example I is dyed under pressure at C. for 2 hours with 3%, based on iiber weight, of Latyl Blue FL Dye (listed in the Technical Manual and Year Book of the American Association of Textile Chemists and Colourists, 1956, p. 215) in the presence of 15%, based on ber weight, of a mixture of 50% dimethyl terephthalate and 50% benzanilide. The resulting thread, which is dyed blue, appears to exhibit no change in length when heated at C. in the absence of tension; how ever, it has a yield strength for 15% permanent deformation of only 0.033 g.p.d. at 160 C. The dyed Thread A is then used as the bobbin thread and Thread B of Example I is used as the needle thread in the sewing machine of Example I to sew a seam joining two layers of the nylon tateta fabric of Example I. The seam contains 18 stitches per inch and the machine is operated at the rate of 5,000 stitches per minute. The seam, which has an as-sewn pucker rating of 1.30%, is pressed with a steam iron at 160 C., whereupon its pucker rating drops to 0.33%. The seam is then subjected to 5 cycles of laundering in 160 F. water and drying at 210 F. without subsequent ironing. At the end of this treatment the seam has developed a pucker rating of only 0.87%. As stated in Example I, in a control experiment in which Thread B is used both in the needle and in the bobbin, the as-sewn seam has a pucker rating of 1.73%, the pressed seam has a pucker rating of 1.45 and the laundered seam has a pucker rating of 2.32%.

It will be apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claim.

l claim:

A scam comprising a plurality of superimposed fabric layers which are substantially stable against dimensional elongation in normal laundering and pressing operations, a synthetic polymer thread penetrating the said layers at regular intervals and extending along the surface of the said fabric layers and interlocked to form a series of stitches, the said thread being permanently elongated dur ing ordinary pressing operation at a tension of less than about 0.1 gm. at least with respect to the distance between thc penetrations along its normally visible length substantially parallel to the surface of 'the fabric layers by pressing with a hot iron at a temperature of at least 160 C., to form a permanent non-puckerable seam upon subsequent launderings.

References Cited in the le of this patent UNITED STATES PATENTS 2,539,244 Halden Ian. 23, 1951 2,714,758 Woodson Aug. 9, 1955 2,731,788 Donaldson Ian. 24, 1956 FOREIGN PATENTS 513,354 Great Britain Oct. 10, 1939 OTHER REFERENCES The Textile Mfger., September 1955, page 493, from the article Stabilization of Structures Made from Polyester Fibers. 

